台阶后退式开挖对基坑围护桩的变形影响分析

Analysis of Influence of Step Backward Excavation on Deformation of Foundation Pit Retaining Pile

结合合肥某地铁车站深基坑实例,利用数值模拟方法研究分层开挖和台阶后退式开挖对围护桩的影响,同时将计算结果与监测数据进行比较。结果表明:采用台阶后退式开挖的数值模拟更能反映实际工程中围护桩的侧移变化情况。基坑两侧围护桩的侧移随台阶后退式开挖呈现明显的时空效应。随着台阶式开挖有沿基坑长度方向上的侧移和基坑宽度方向上的侧移,沿基坑长度方向上的侧移近似呈椭圆形向后扩散,直至开挖至端头井处呈现半椭圆形状,沿基坑宽度方向上的侧移近似呈半椭圆形向后扩散;围护桩的侧移峰值和其深度随周围开挖土体深度的增加而增加,直至开挖土体远离该围护桩时趋于稳定。

Combined with a deep foundation pit of a subway station in Hefei, the numerical simulation method is used to study the influence of layered excavation and step backward excavation on retaining pile. At the same time, the calculation results are compared with the monitoring data. The results show that the numerical simulation of step back excavation can better reflect the lateral displacement of retaining pile in practical engineering. The lateral displacement of retaining piles on both sides of the foundation pit presents obvious time-space effect with the step backward excavation. Step backward excavation has lateral displacement along the length direction of foundation pit and lateral displacement along the width direction of foundation pit. The lateral displacement along the length direction of foundation pit is approximately elliptical and diffuses backward until it reaches the end well and presents a semi-elliptical shape. The lateral displacement along the width direction of foundation pit is approximately a semi-ellipse and diffuses backward. The peak value of lateral displacement and its depth of retaining pile increase with the depth of surrounding excavation soil, and tend to be stable when the excavation soil is far away from the retaining pile.